memory_usage.h

#pragma once
 
#include <concepts>
#include <cstddef>
#include <optional>
#include <vector>
 
namespace pixie {

template <class T, class Allocator>
std::size_t vector_capacity_bytes(const std::vector<T, Allocator>& values) {
  return values.capacity() * sizeof(T);
}

template <class T>
concept HasMemoryUsageBytes = requires(const T& value) {
  { value.memory_usage_bytes() } -> std::convertible_to<std::size_t>;
};

template <HasMemoryUsageBytes T>
std::size_t nested_owned_memory_bytes(const T& value) {
  const std::size_t total = value.memory_usage_bytes();
  return total > sizeof(T) ? total - sizeof(T) : 0;
}

template <HasMemoryUsageBytes T>
std::size_t optional_nested_owned_memory_bytes(const std::optional<T>& value) {
  return value.has_value() ? nested_owned_memory_bytes(*value) : 0;
}
 
}  // namespace pixie